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Uniparental Disomy

Does this test have other names?

Genetic testing for Angelman syndrome, genetic testing for Prader-Willi syndrome

What is this test?

This is a blood test used to see if your child has certain chromosome changes.

Normally, people have 23 pairs of chromosomes in their cells. In each pair, one chromosome comes from their father and one from their mother. These chromosomes contain genes.

Sometimes people will inherit 2 copies of a chromosome or a part of a chromosome from their mother or father, but none from their other parent. This is called uniparental disomy. In some cases this causes health problems.

Two health conditions that are often linked to uniparental disomy are Prader-Willi syndrome and Angelman syndrome. In some of these cases, the person is missing chromosome 15 from one parent. This blood test can help find out if a child has uniparental disomy related to one of these syndromes. 

Why does my child need this test?

Children may have genetic testing to help diagnose them with Prader-Willi or Angelman syndrome. Making the diagnosis of Prader-Willi or Angelman syndrome early in life can help healthcare providers and parents plan for early intervention.

Symptoms of Prader-Willi syndrome often include:

  • Difficulty feeding as a baby with poor weight gain. But the child has a very strong appetite as a toddler.

  • Obesity

  • Undescended testicles and small penis in boys

  • Learning and behavior problems

  • Delayed puberty and abnormal sexual development

Symptoms of Angelman syndrome often include:

  • Small head size

  • Developmental problems

  • Unusually frequent laughing and smiling

  • Notably happy and excitable demeanor

  • Frequent flapping hand gestures

  • Trouble communicating

  • Trouble walking

  • Seizures

What other tests might my child have along with this test?

A child's symptoms help healthcare providers make a diagnosis of Prader-Willi or Angelman syndrome. Your child may need several genetic tests to confirm the diagnosis and figure out if symptoms are caused by uniparental disomy. 

What do my child's test results mean?

Test results may vary depending on your child's age, gender, health history, the method used for the test, and other things. Your child's test results may not mean they have a problem. Ask your child's healthcare provider what the test results mean for your child.

The results of gene testing can tell you if your child has one of these disorders. The results can also tell whether uniparental disomy is the cause. The cause of the syndrome may link to how the problem affects your child. For instance, when uniparental disomy is the cause of Angelman syndrome, children are less likely to have a small head, seizures, and certain other problems. 

How is this test done?

The test is done with a blood sample. A needle is used to draw blood from a vein in your child's arm or hand. A blood sample from your child and both parents may be needed.

Does this test pose any risks?

Having a blood test with a needle carries some risks. These include bleeding, infection, bruising, and feeling lightheaded. When the needle pricks your child's arm or hand, they may feel a slight sting or pain. Afterward, the site may be sore.

What might affect my child's test results?

No medicines or conditions will affect your child's test results.  

How do I get my child ready for this test?

Your child doesn't need to get ready for this test. 

Online Medical Reviewer: Fetterman, Anne, RN, BSN
Online Medical Reviewer: Haldeman-Englert, Chad, MD
Date Last Reviewed: 6/1/2018
© 2000-2018 The StayWell Company, LLC. 800 Township Line Road, Yardley, PA 19067. All rights reserved. This information is not intended as a substitute for professional medical care. Always follow your healthcare professional's instructions.